The present invention relates to heat pumps and heat transfer components therein, and in particular, to a plate incorporating a heat pipe across which high efficiency heat transfer may take place.
The need for energy conservation has been highlighted by concerns about the environment, leading to improvements in energy efficient heating and cooling systems. Increased attention has been directed to the development of efficient, cost-effective absorption heat pumps which use waste heat for heating and cooling and, thus, reduce energy consumption. The use of waste heat allows absorption heat pumps to deliver more energy to a heated space than they extract from an electric power grid or other high grade energy source. As a result, absorption heat pumps are gaining favor over the more conventional vapor compression heat pumps which are driven almost entirely by electric power.
Other environmental concerns favor the use of absorption heat pumps because they generate less noise and, more importantly, use fluids other than the chlorofluorocarbon refrigerants used in vapor compression heat pumps. Bans on chlorofluorocarbon refrigerants which cause injury to the earth's ozone layer have made absorption heat pumps increasingly more attractive.
Vapor-absorption heat pumps may operate in accordance with any of several vapor-absorption cycles known in the art, such as single or multi-stage cycles. As well, vapor-absorption heat pumps may operate at positive pressures or sub-atmospheric pressures, depending on the fluids used therein. Regardless, vapor-absorption heat pumps typically include an evaporator, an absorber, a vapor generator and a condenser and, preferably, additional heat exchangers. These heat pump components typically include heat transfer surfaces which may be fixed or moving. Fixed heat transfer surfaces are provided, for example, in that group of heat pumps generally referred to as falling film devices, which rely on gravity to distribute fluid across surfaces between which heat transfer takes place. More recent developments in the art have related to heat pumps having moving or rotating heat transfer surfaces.
In U.S. Pat. No. 4,553,408 (the '408 patent), Cross et al disclose a compact absorption heat pump in which at least one of the heat pump components comprises one or more rotatable plates across which heat transfer takes place. Such plates must be thin enough to permit high thermal flux from one face to another, but thick enough to provide necessary rigidity in operation. Thus, while they may be generally between 0.1 millimeters (mm) and 5 mm in thickness, they are typically between 0.25 mm and 1.25 mm thick to provide needed rigidity. Such plates are made of thermally conductive materials, typically mild steel, stainless steel, copper and aluminum.
Because of the significant role heat transfer surfaces play in heat pumps, such as the rotating plates in the compact, cost-effective absorption heat pump of the '408 patent, improvements in heat transfer efficiency across such plates are sought to provide further significant improvement in system performance and produce even greater energy savings.